1. Field of the Invention
The present invention relates to a method for manufacturing an elongate structural element configured for stiffening a shell structure, and to a method for manufacturing a rigid shell structure integrated with at least one elongate stiffening element. Preferably, such methods are related to use of curable composite materials, such as fiber-reinforced composite materials, carbon fiber epoxies, etc.
2. Related Art
The manufacturing of structural elements used for the construction of vehicles, vessels and aircraft often requires high strength, light-weight composite materials containing a plurality of curable layers of fibers and metal joined by adhesive thermoset and thermoplastics. Conventionally, structural elements of composite materials are manufactured by arranging a former made of metal on a base plate and laying up laminate layers of so-called “prepeg” on the former. Then, the base plate, former and laminate material are encapsulated in one or more vacuum bags before inserting the assembly into a pressure tank in order to increase the pressure acting on the composite material in the tank and to cure the structural element. The curing of the structural element may also take place in a so-called autoclave, or possibly in an oven.
Previously known methods of manufacturing structural elements of more complex shapes, for example curved elongate hat profiles configured for stiffening a shell structure, often require destructible formers (e.g. so-called “Stabilam”) in order to be able to remove the finished element therefrom.
For example, the EP application No. 05002075.9, not published before the present application, describes use of a water-soluble former when manufacturing an elongate hat or omega-profiled structural elements, such as stiffeners, spars, fittings or the like. This involves further manufacturing steps. Also, in such elongate hat or omega-shaped profiles high shearing and splitting stresses are often exerted on the outwardly directed flanges of the finished structural element which calls for a more rigid structure.
U.S. Pat. No. 6,458,309 B1 discloses a method for fabrication of composite aerostructure articles wherein an elongated hollow mandrel made of a pre-stiffened, flexible, spirally arranged tape is used as a former for hat-profiled reinforcement sections of a shell structure. However, although the former may remain in the finished article as a “fly-away tool”, a spring-like flexibility of the hollow mandrel makes it not able to take up any greater loads, especially not in the longitudinal direction of the hat profile.